The specific aims of this proposal are divided into three phases: (1) to identify first and second degree relatives of patients with IDDM who are prediabetic by measuring islet cell antibody titers; (2) to identify prediabetic relatives who are at high risk to develop IDDM; (3) to prevent or delay the onset of IDDM in high risk relatives by administering intravenous and subcutaneous insulin in a clinical trial.